Former psychiatrists and social workers employed on Nauru are demanding a Royal Commission into sexual abuse at the Australian-funded detention centre, accusing the Government of putting asylum seeker children at risk.

The former Nauru workers have signed an open letter to the public, which says the Immigration Department was aware of abuse allegations for 17 months and did not respond adequately.

One of the signatories, Viktoria Vibhakar, a former child protection worker with the charity Save The Children, has broken her silence in an exclusive interview with Lateline.

Ms Vibhakar pointed to some of the worst examples from Nauru to highlight the need for a Royal Commission:

A girl under the age of 11 who said she was sexually assaulted, and later self-harmed.

A boy about seven years old who was found naked in the middle of the night outside a tent.

A girl about five years old who exhibited sexualised behaviour, including asking adults to insert items into her anus.

Ms Vibhakar did not specify the children's exact ages to help protect their identities.

The signatories say the Federal Government was aware of abuse allegations as early as November 2013.

"What the public needs to know is that the Government has been aware for 17 months that children have been sexually assaulted on Nauru," Ms Vibhakar told Lateline.

Ms Vibhakar said she resigned in disgust because she felt her role as clinical social worker was "ethically compromised".

Shortly after she quit, the Immigration Department ordered her off the island along with nine other Save The Children workers amid allegations contractors had facilitated protests and fabricated sexual abuse allegations.

An independent inquiry by former Integrity Commissioner Philip Moss found no evidence of misconduct by Save The Children workers.

Former workers including Ms Vibhakar have slammed the Government's pursuit of the group.

"The Government was more interested in a smokescreen to really change the dialogue, change the conversation nationally about what was happening in Nauru," she said.

Ms Vibhakar said she was not interviewed by Mr Moss.

Children 'mimicked sexual intercourse with each other'

Two other former Save The Children workers who have spoken to Lateline on the condition of anonymity say they were alarmed by the extent of sexualised behaviour among asylum seeker children.

In one example, one of the former workers said children as young as six would mimic sexual intercourse with each other.

"We're talking about kids saying what they refer to as jiggy jiggy and they would pretend to hump another child," he said.

He also said a group of boys had learnt an insult describing an explicit sex act from Nauruan security officers.

"There was children under the age of 10 that would joke around with a graphic description of an act of a man coming inside a woman," he said.

Some of the offenders identified by the Moss inquiry were locally hired Nauruans.

A third former worker said a number of Nauruans had continued to threaten a teenage boy and his family, after he reported being sexually assaulted by a Nauruan employee, who was sacked as a result.

The Moss inquiry noted Nauru had no compulsory working with children checks and no mandatory requirement for reporting child abuse.

"There is no way of actually doing checks on all local staff. Children remain at risk (and) potentially there could be further sex offenders in the centre," the former worker said.

Other signatories to the open letter include psychiatrists Dr Peter Young, Dr Michael Gordon and Dr Rodney Juratowitch, who worked for the immigration medical contractor, IHMS (International Health and Medical Services).

Dr Young, the former head of mental health services in the detention system, said a Royal Commission was needed despite the previous findings of an Australian Human Rights inquiry, the Moss inquiry and now a current Senate inquiry into Nauru.

"I think what we've seen with these other inquiries is that they get accused of being biased or accused of being politicised," he said.

Immigration Minister Peter Dutton said the recent Moss review examined what knowledge the department had of the allegations.

He told Sky News he was seeking further advice on the matter.

"The understanding in terms of the sequence of events that I'm aware of is that the former minister [Scott] Morrison was made aware of allegations late last year. He referred the matter to the then acting secretary of the department, the acting secretary then commissioned Mr Moss to undertake the review," he said.